This invention relates generally to wireless communications, and more particularly, to wireless handheld electronic devices in which monitoring and control circuitry is used to measure wireless signal powers.
Handheld electronic devices are becoming increasingly popular. Examples of handheld devices include handheld computers, cellular telephones, media players, and hybrid devices that include the functionality of multiple devices of this type.
Due in part to their mobile nature, handheld electronic devices are often provided with wireless communications capabilities. Handheld electronic devices may use long-range wireless communications to communicate with wireless base stations. For example, cellular telephones may communicate using cellular telephone bands at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz. Handheld electronic devices may also use short-range wireless communications links. For example, handheld electronic devices may communicate using the WiFi® (IEEE 802.11) band at 2.4 GHz and the Bluetooth® band at 2.4 GHz. Communications are also possible in data service bands such as the 3 G data communications band at 2170 MHz band (commonly referred to as UMTS or Universal Mobile Telecommunications System). Some handheld devices receive Global Positioning System (GPS) signals at 1575 MHz.
A number of compromises are typically made when designing an antenna for a handheld electronic device. For example, antennas that protrude excessively from a device housing may be unsightly. Antennas that are located within a device housing may be more desirable from an esthetic point of view, but can be challenging to design. Internal antennas are sometimes subject to proximity effects that make antenna performance dependent on the position of a user's body relative to the antenna. Moreover, internal antennas may require the use of compact designs that are not as efficient as bulky external antennas.
Compact internal antennas for handheld devices may fabricated by patterning a metal layer on a circuit board substrate or may be formed from a sheet of thin metal using a foil stamping process. Many handheld devices use planar inverted-F antennas (PIFAs). Planar inverted-F antennas are formed by locating a planar resonating element above a ground plane. These techniques can be used to produce antennas that fit within the tight confines of a handheld device.
Although compact antennas may be formed that are suitable for mounting within the interior of a handheld electronic device, such antennas may be subject to proximity effects. For example, if a user places their fingers over the antenna, the antenna may be detuned. This can cause undesirable dropped signals.
It would therefore be desirable to provide handheld electronic devices that can determine when antennas are blocked by a user's hand and can take appropriate actions.